Chlorination of Hydrogenated Silicon Nanosheets Revealed by Solid-State Nuclear Magnetic Resonance Spectroscopy

Two-dimensional silicon nanosheets (Si-NS) synthesized
by topotactic
deintercalation of CaSi2 are hypothesized to consist of
buckled layers of sp3-hybridized silicon atoms that are
bonded to three other framework Si atoms and a terminal atom or functional
group such as H, Cl, or OH. Here, we apply 1H{35Cl} and 29Si{35Cl} Resonance-Echo Saturation-Pulse
DOuble-Resonance (RESPDOR) solid-state NMR experiments to directly
confirm the presence of chlorinated Si atoms within Si-NS. Plotting
the 1H{35Cl} RESPDOR dephasing as a function
of the 35Cl saturation pulse offset reveals that the 35Cl quadrupolar coupling constant (CQ) is 38 MHz, consistent with Cl atoms that are covalently
bonded to silicon. Modeling the 1H{35Cl} RESPDOR
dephasing curve shows that the Si–Si interlayer spacing is
approximately 6 Å. Plane-wave density functional theory (DFT)
calculations show that the direct band gap transition of the Si-NS
decreases with increasing chlorination and hydroxylation, suggesting
that the band gap of Si-NS can be tuned by modifying the terminal
atoms or functional groups.